Generally, a device that blocks cellular phone signals is known as a cell phone jammer. This device may also be referred to as a signal blocker or text stopper.
A cell phone jammer is a device designed to interfere with communication over the air waves. This equipment uses radio frequency to disrupt the signals that telecommunication towers transmit over a geographic area. A jammer works by getting on the same frequency as a mobile phone and preventing the device from connecting to a cellular network. This occurs due to the louder signal being emitted by the jammer, which provides interference and hinders a cell phone from accessing cell tower service.
In the United States, a cell jammer is considered to be an illegal device as of 2015. Under federal law, civilians and commercial establishments that are caught operating any type of jamming device are subject to monetary sanctions, seizure of the illegal device and even jail time, notes FCC.gov.
Jamming technology is said to pose serious security threats to crucial public safety communications, such as reaching 911 for emergency situations. A jammer can also potentially interfere with critical police operations that require radio communication. Aside from banning the operation of cell jammers, the U.S. government also criminalizes the marketing, selling, renting, importing, exporting and distribution of these devices.